Project The Neglected Honda project...

Yes, you have to wind it back in before you re-install and it then pushes out to pressure itself.

 

So after a bit more playing I'm now convinced the timing is correct, 1 tooth out in either direction makes it worse. When the CCT isn't installed there's a bit of slack on the intake side, when you push it with your finger it moves the cams that little bit and makes the timing look a little off. I'll upload a video later so you can see what I mean.

As for why the thing doesn't start, that one exhaust valve that was "just" out of spec is now proving to be MORE out of spec. I don't know how that's even possible. I reduced the shim size from 2.05 to 1.88 which I thought was MORE than enough (0.17 reduction when I am targeting a clearance of 0.15) and now it is somewhere between 0.10 and 0.11 so I need to take it down another 0.05. How is that logically possible... it's like it's expanded so much it was putting upwards pressure on the cam - surely that would start cracking/damaging the bucket...

So that is a puzzle but I'll get a new shim and see how it goes I guess, before I go digging into the ring situation anyway.

 

Yeh they're tight, always do them up before I check clearances. The CCT is fine it tensions up OK, I've ordered a 1.82mm shim so hopefully that last valve will come within spec. I've heard this bike is a bit temperamental to start anyway so maybe that one valve is causing problems.

If I don't get some love then it's next steps (carbies again, new plug, ring investigation). People keep telling me I shouldn't have a ring issue as these engines should take a bit of abuse but i suppose because it is air cooled and someone was sitting in traffic revving the living crap out of it, it's only a matter of time before you overheat. Rings are only $70 for a set genuine anyway, hope I don't have to do them because I really can't be bothered but I suppose that's the risk you take when you gamble on a bike that doesn't run!

 

It's a good thought, cheers. I'll have a look at the wiring diagram and see if there's a possible issue. I know there's an issue with that one valve so once I fix that if compression tests OK then it must be some other issue.

 

So I think today has been an eventful day.

I fitted the new 0.82mm shim on that one valve that was 0.10mm. That should be an increase in the clearance by 0.06mm (ie my target was 0.16 clearance). When I reassembled back together I measured it up... 0.13mm. Weird, huh? The clearance only changed by 0.03mm.

Started to piece together a theory then, but had to test said theory... so compression test kit comes out, throttle open

1. 35 PSI
2. 35 PSI
3. 35 PSI

At least it's consistent, but weirdly very low. Added a spoonful of oil down the plug hole

4. 40 PSI
5. 45 PSI
6. 42 PSI

I think I can safely say that the oil didn't make much difference, so can be relatively confident it's not the rings. If it's not the rings the low compression can only be the valves.

So thinking back to everything undertaken, I think this scenario makes sense:

The dumbo who had this bike previously didn't service it (or properly) because it is due to have clearances done very early in its life (and apparently these get clearance issues quite regularly). If you remember the exhaust valves were both WAY out of spec, one at almost no clearance and one very close to none. If you run the bike in a scenario like that what will happen is that the valve is held open too long in the cycle and there is a risk of it hitting the piston. If that happens a few things could eventuate but I think in this particular scenario it's bent that exhaust valve with the strange clearance. That would also cause compression loss and explain my challenges in getting it to the correct clearance.

So next step is to pull the head off and confirm that suspicion. Long weekend coming up - single cylinder bike... parts will probably be the hardest/most time consuming thing.

Any advice from people who have dealt with bent valves before? I am assuming the head will need to be inspected, everything measured up and possibly a new valve cut into the seat. Not sure I have the precision tools to confirm all this myself though, I could pull the valves out easy enough but it would require a cylinder head expert to rectify I imagine.

 

Thanks guys.

I have a valve lapping kit already, I would just need to source a valve as I agree straightening may end up being a problem later (hard to see microfractures from the first signs of fatigue etc without some very powerful glasses!). Hopefully it's that one exhaust valve and the seat is in OK condition. I'll let you know how I go.

@Phil, looks like they need attention at 12 months or 12,000 kms, 24,000 kms or 2 years etc. 'I' in the legend means inspect, adjust as required etc so if the guy didn't service it and it had a bit of a rough time early on, it's missed at least three checks already.

View attachment 18077

 

Play this first, it goes well with the photos haha...























So maybe bent, maybe not. Weird thing to happen though...

 

Anyone bought one of these before?

http://www.ebay.com.au/itm/10PC-Val...055415?hash=item4aec7adf37:g:G3sAAOSw9N1VkPcw